Antibody staining was observed in the electron microscope by means of untagged antibody and osmium fixation. The antibody was visualized as a change in morphology due to its deposition on the antigenic structures. Glycerinated chicken breast muscle was stained with antimyosin, anti-H-meromyosin, and antiactin. The staining patterns obtained by electron microscopy were consistent with those previously demonstrated by fluorescence microscopy. A second method was used for confirmation of antibody staining. This consisted of extraction of unstained portions of the sarcomere with 0.6 M potassium iodide, 10-4 M adenosine triphosphate solution. Stained regions of the sarcomere remained intact because of insolubility of the combined antigen and antibody.